I can understand that desire, but think about this from a practical perspective. You are on lemmy.world, but someone else is on lemmy.ml. If you both use the same app that does this behind the scenes aggregation for you, you won’t be able to tell which instance is holding which post. Let’s say someone on sh.itjust.works posts on their instance of a community, but the app just makes it appear like it’s in the community.

Now, if lemmy.world blocks sh.itjust.works and lemmy.ml does not, then you can’t see that post, since it’s blocked for you. But the person on lemmy.ml and on sh.itjust.works would be able to see it. This is a good example of solving a problem by create a dozen new ones.

Lemmy developers have been discussing how to address this: https://github.com/LemmyNet/lemmy/issues/818

There isn’t a clear solution, since some communities have different names, so how would an app know to join them? Or would you join communities that had deliberately been split for various reasons?

I’m sure the apps developed for Lemmy will ‘combine’ those behind the scenes for a smoother user experience.

I don’t think that’s a good idea, it would give the impression of something that is not there. Imagine talking to someone about a post that you just read but that someone else literally can’t see because they aren’t using the app, so they can’t see that instance. Plus, how do you handle communities on instances that have been blocked by some other instances?

A better way would be to have a way to officially merge these communities within ActivityPub. Effectively, have a protocol for cross instance communities, and then the mods of the disparate communities would just have to actively choose to join their communities. It’d be like the reddit sub splitting, but in reverse!